Depolarized Rayleigh-Brillouin scattering is used to investigate the isomers of the homologous alkane series n-pentane to n-octane. In addition to the low frequency lorentzian component, associated with molecular reorientation, a second lorentzian component is found in the spectra from the liquids 2,2,4-trimethylpentane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 2,2,3-trimethylbutane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, n-pentane and 2-methylbutane. The contribution to the spectra of this second lorentzian, which is broader than the lorentzian associated with molecular reorientation and distinct from the interaction induced component, reduces as the molecules become more anisotropic and flexible.